The method of solution uses superposition
coupled with an orthonormalization procedure and a variable-step
Runge-Kutta-Fehlberg integration scheme. Each time the
superposition solutions start to lose their numerical
independence, the vectors are reorthonormalized before integration
proceeds. The underlying principle of the algorithm is then to
piece together the intermediate (orthogonalized) solutions,
defined on the various subintervals, to obtain the desired
solution.

The
user must supply subroutines FMAT and GVEC to evaluate
derivatives.
The CDC6600 version contains a COMPASS as well as a FORTRAN
version of function DOTPRO. DOTPRO computes the inner product of
two vectors. Whenever possible, an Assembly coded version of this
subroutine should be used.
There are several machine-dependent constants used throughout
the code. These are listed in the comment section of the code
along with the suggested values for other computers. Except for
these constants, the code is virtually machine-independent.